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Allergen: A substance that triggers an allergic reaction.

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Allergic Rhinitis: An allergy affecting the mucus membrane of the nose. Seasonal allergic rhinitis is often called "hay fever."

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Allergist: A doctor that diagnoses, treats, and manages allergy-related conditions.

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Ana-Kit: A device used to inject epinephrine during an anaphylaxis attack.

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Anaphylaxis: A life-threatening allergic reaction that involves the entire body. Anaphylaxis may result in shock or death, and thus requires immediate medical attention

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Animal dander: The small scales or pieces of skin, often containing proteins secreted by oil glands, which are shed by an animal. These proteins are the major causes of allergies to pets.

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Antibiotics: A class of medications used to treat bacterial infections. Certain antibiotics, such as penicillin, may cause an allergic reaction in some people.

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Antibody: A protein in the immune system that recognizes and attacks foreign substances in the body.

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Anticonvulsant: A medication used to prevent or treat seizures. Certain anticonvulsants may cause an allergic reaction in some people.

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Antihistamines: A class of medications used to block the action of histamines in the body and prevent the symptoms of an allergic reaction.

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Asthma: An inflammatory disorder of the airways, causing periodic attacks of wheezing, coughing, chest tightness, and shortness of breath.

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Atopic dermatitis: A chronic skin rash, also known as "eczema," that often appears in the first few years of life.

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Basophil: An immune system cell that attaches to antibodies and circulates through out the blood.

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Beta-blockers: A class of blood pressure medications that ease the heart's pumping action and widen the blood vessels. Beta-blockers counteract the effects of epinephrine used for emergency treatment of anaphylactic shock and should not be used during immunotherapy.

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Bronchial tubes: The lower sections of the airway that lead into the lungs.

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Challenge test: A test used to confirm an allergy to specific substance. A doctor will administer small but increasing amounts of a suspected allergen until an allergic response is noticed. Due to the risk of anaphylaxis, this should only be performed under a controlled setting.

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Conjunctivitis: Inflammation of the conjunctiva, or the mucous membrane surrounding the eye. Also known as pinkeye.

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Contact dermatitis: An allergic reaction resulting from skin contact to an allergen.

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Corticosteroid: An anti-inflammatory medication used to treat the itching and swelling associated with some allergic reactions.

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Cromolym sodium: An anti-inflammatory nasal spray used to treat and sometimes prevent allergic rhinitis.

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Decongestants: A class of medications used for nasal congestion. Decongestants are available in oral doses, nasal sprays, or eye drops (for conjunctivitis).

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Dust mites: A microscopic organism that lives in dust.

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Eczema: See Atopic dermatitis.

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Eosinophil: A specific type of immune cell that can cause tissue damage in the late phase of an allergic reaction.

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Epinepherine: A medication used for immediate treatment of anaphylaxis by raising blood pressure and heart rate back to normal levels. Epinepherine is also known as adrenaline.

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EpiPen: A device used to inject epinephrine during an anaphylaxis attack.

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Heparin: A chemical released by basophils and mast cells that causes nearby tissues to become swollen and inflamed.

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Histamine: A chemical released by basophils and mast cells that causes nearby tissues to become swollen and inflamed.

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Hives: See urticaria.

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Hypertension: High blood pressure. When blood pushes against artery walls harder than normal.

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Immunoglobulin E: A type of antibody responsible for most allergic reactions.

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Immunotherapy: A series of shots that help build up the immune system's tolerance to an allergen.

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Insulin: A hormone that regulates blood sugar levels. Diabetics who take insulin derived from animals may have allergic reactions.

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Intradermal test: A test where an allergen is injected just underneath the skin. Intradermal tests are generally used when results from a skin prick test are unclear.

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Late Phase: The period 4 - 24 hours after exposure to an allergen where tissue damage may occur.

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Leukotrienes: Inflammatory substances that are released by mast cells during an allergic response or asthma attack.

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Lymphocyte: A specific type of immune cell that can cause tissue damage in the late phase of an allergic reaction.

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Mast cell: An immune system cell which attaches to antibodies and is located in the tissue that lines the nose, bronchial tubes, gastrointestinal tract, and the skin

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Neocromil sodium: An inhaled medication used to treat inflammation involved with asthma.

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Neutrophil: A specific type of immune cell that can cause tissue damage in the late phase of an allergic reaction.

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Otitis media: A middle ear infection. Otitis media with effusion occurs when fluid builds up within the ear.

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Radioallergosorbant Test (RAST): A blood test that measures the amount of IgE antibody produced when the sample is mixed with a specific allergen.

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Rhinitis: An inflammation of the nasal passageways, particularly with discharge.

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Sinusitis: An inflammation or infection of one or more sinuses. The sinuses are hollow air spaces located around the nose and eyes.

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Skin prick test: A test where a needle is used to scratch the skin with a small amount of allergen. A response can usually be seen within 15 - 20 minutes.

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Urticaria: Raised areas of the skin that are often red, warm, and itchy. Urticaria is also known as hives.

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Urushiol: An oil found on poison ivy, oak, and sumac.

Each spring, summer, and fall, tiny pollen grains are released from trees, weeds, and grasses. These grains hitch rides on currents of air. Although the mission of pollen is to fertilize parts of other plants, many never reach their targets. Instead, pollen enters human noses and throats, triggering a type of seasonal allergic rhinitis called pollen allergy. Many people know this as hay fever.

Of all the things that can cause an allergy, pollen is one of the most common. Many of the foods, medicines, or animals that cause allergies can be avoided to a great extent. Even insects and household dust are escapable. But short of staying indoors when the pollen count is high -- with the windows closed, there is no easy way to avoid airborne pollen.

What is pollen?

Plants produce microscopic round or oval grains of pollen, which are used for reproduction. In some species, the plant uses the pollen from its own flowers to fertilize itself. Other types must be cross pollinated. Cross-pollination means that, for fertilization to take place and seeds to form, pollen must be transferred from the flower of one plant to that of another of the same species. Insects do this job for certain flowering plants, while other plants rely on the wind for transport.

The types of pollen that most commonly cause allergic reactions are produced by plain-looking plants (trees, grasses, and weeds) that make small, light, dry pollen grains that are spread by the wind.

Scientists have collected samples of ragweed pollen 400 miles out at sea and 2 miles high in the air. Because airborne pollen can drift for many miles, it does little good to rid an area of an offending plant. In addition, most allergenic pollen comes from plants that produce it in huge quantities. For example, a single ragweed plant can generate a million grains of pollen a day.

The type of allergens in the pollen determine whether the pollen may cause hay fever. It might seem that pine tree pollen, which is produced in large amounts by a common tree, would make it a good candidate for causing allergy. It is, however, less allergenic than other plants, and a relatively rare cause of allergy. Because pine pollen is heavy, it tends to fall straight down from the tree and does not scatter in the wind, rarely reaching human noses.

Among North American plants, weeds are the biggest producers of allergenic pollen. Ragweed is the major culprit, but other important sources are sagebrush, redroot pigweed, lamb's quarters, Russian thistle (tumbleweed), and English plantain. Grasses and trees, too, are important sources of allergenic pollens. Those that produce highly allergenic pollen include timothy grass, Kentucky bluegrass, Johnson grass, Bermuda grass, redtop grass, orchard grass, and sweet vernal grass. Trees that produce allergenic pollen include oak, ash, elm, hickory, pecan, box elder, and mountain cedar.

It is common to hear people say that they are allergic to colorful or scented flowers like roses. In fact, only florists, gardeners, and others who have prolonged, close contact with flowers are likely to be sensitive to pollen from these plants. Most people have little contact with the large, heavy, waxy pollen grains of such flowering plants because this type of pollen is not carried by wind but by insects such as butterflies and bees.

"I love springtime, but the pollen drives me up the wall! I start taking my medication as soon as I see buds on the trees."

-- Esther, age 39

When do plants make pollen?

One of the most obvious features of pollen allergy is its seasonal nature -- people have symptoms only when the pollen grains to which they are allergic are in the air. Each plant has a pollination period that is more or less the same from year to year. Exactly when a plant starts to pollinate seems to depend on the relative length of night and day -- and therefore on geographical location -- rather than on the weather. On the other hand, weather conditions during pollination can affect the amount of pollen produced and distributed in a specific year. Thus, in the Northern Hemisphere, the farther north you go, the later the start of the pollinating period and the later the start of the allergy season.

A pollen count, familiar to many people from local weather reports, is a measure of how much pollen is in the air. This count represents the concentration of all the pollen (or of one particular type, like ragweed) in the air in a certain area at a specific time. It is shown in grains of pollen per square meter of air collected over 24 hours. Pollen counts tend to be the highest early in the morning on warm, dry, breezy days and lowest during chilly, wet periods. Although the pollen count is an approximate measure that changes, it is useful as a general guide for when it may be wise to stay indoors and avoid contact with the pollen.

Created by the National Institutes of Health. Illustration copyright A.D.A.M., Inc.

 

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Review Date: 4/4/2007

Reviewed By: Alan Greene, M.D., F.A.A.P., Department of Pediatrics, Packard Children's Hospital, Stanford University School of Medicine; Chief Medical Officer, A.D.A.M., Inc.


The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

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